Twin 16-year-old sisters and their father were shot and killed in what appears to be a murder-suicide inside their St. Charles, Illinois, home, according to several reports.

The Associated Press reports authorities were called to a luxury condominium complex shortly after 5 p.m. on Friday by someone inside the home as well as neighbors who heard gunshots from inside the home.

Deputy Chief David Kintz named those who died as Brittany and Tiffany Coffland, both age 16, and their father, 48-year-old Randall R. Coffland. The teens’ mother, Anjum Coffland, was shot and remains at the local Delnor Community Hospital in stable condition.

Police tell the Associated Press that they believe Randall shot his family in what appeared to be a murder-suicide.

“It’s kind of unnerving to realize that someone you were so close with, and could see in a day, and could be gone in a matter of hours,” Ally Siebrasse, a friend of the slain sisters, who were juniors at St. Charles East High School, told WGNTV.

“Tiffany would just absolutely light up a room with her smile. Her personality. She was an amazing young girl. You could tell made everyone better just by knowing her,” Siebrasse said, while Brittany, a cheerleader, was “kindhearted.”

Police said Anjum and Randall were married but living at separate addresses, according to AP.

Want to keep up with the latest crime coverage? Click here to get breaking crime news, ongoing trial coverage and details of intriguing unsolved cases in the True Crime Newsletter.

The Daily Herald reports that officers responded to a report of domestic trouble Feb. 9 on the 100 block of South 5th Avenue in St. Charles. The report indicated that “nothing physical happened” during the previous incident, police said.

Authorities declined to release the Feb. 9 report or address who fired the shots on Friday, the outlet reports.

One neighbor told WGNTV said she felt something was off that night.

“When I walked across the street I had heard screams,” Tammy Hartje said. “I looked up and I noticed in that apartment they had the door open and I was thinking that’s weird because it was so cold outside.”

Mourners have been contributing to a memorial on a bench near the scene, laying flowers and candles throughout the weekend, according to the Daily Herald. Three wooden crosses with the names of the deceased were placed in front of the bench.

• Pick up PEOPLE’s special edition True Crime Stories: Cases That Shocked America, on sale now, for the latest on Casey Anthony, JonBenét Ramsey and more.

Tatianna Lerario, who was also on the high school’s cheer squad, told the outlet there didn’t seem to be any signs of trouble when she visited the Coffland family.

“I guess you really don’t know what happens on the inside,” Lerario added. “No one does.”